In current wireless communication networks, e.g., based on the LTE (Long Term Evolution) cellular radio access technology specified by 3GPP (3rd Generation Partnership Project), carriers from various frequency spectra may be utilized for performing radio transmissions. Typically, these carriers are selected from a frequency spectrum which is licensed to an operator of the wireless communication network.
To further improve the performance of LTE systems, extension of the LTE technology to unlicensed frequency spectra is being considered. This concept is also referred to as Licensed Assisted Access (LAA). For operation in an unlicensed frequency spectrum, certain compliance with certain requirements is typically considered necessary. One such requirement is that a transmitter needs to listen on a carrier utilized before it starts to transmit on this carrier. If the carrier is free, the transmitter can perform a radio transmission on the carrier. On the other hand, if the carrier is busy, e.g., because some other node is transmitting on the carrier, the transmitter needs to suppress the transmission and may retry gaining access to the carrier at a later time. This procedure is referred to as “listen before talk” (LBT). Corresponding issues are for example discussed in 3GPP TR 36.889 V13.0.0 (2015-06).
In the case of not gaining access to the carrier through the LBT procedure, the transmitter needs to delay a planned radio transmission until the carrier becomes free. This may involve multiple attempts of gaining access to the carrier and multiple LBT procedures. However, even if the carrier becomes free at some time, it may happen that the transmitter is not able to gain access to the carrier because some other node managed to occupy the carrier before the transmitter. This may result in undesirable accumulation of delays before the transmitter eventually succeeds in performing the LBT procedure at a time when the carrier is free. Accordingly, there is a need for techniques which allow for efficiently controlling LBT based radio transmission.